PROJECT SUMMARY/ABSTRACT Aging-related changes to the structure and function of the heart increase vulnerability to cardiovascular disease (e.g., heart disease, stroke), frailty, falls, dementia, and Alzheimer disease. Exercise-based cardiac rehabilitation (CR) slows these processes, reduces risk of mortality, and improves physical function and quality of life. However, most patients who enroll in CR fail to gain the full benefits of treatment due to poor attendance and adherence, and few maintain independent physical activity when CR treatment ends. Exercise anxiety is a novel mechanism related to non-adherence to exercise and lifestyle physical activity that is characterized by cognitive, behavioral, and physiological underpinnings. Exercise anxiety is particularly elevated in patients enrolled in CR given that physical sensations of exercise often feel similar to sensations attributed to cardiovascular disease (e.g., shortness of breath, racing heart). Heightened awareness of these bodily sensations can promote fear and worry about what could happen during exercise (e.g., “What if I have a heart attack?”), even though it is both safe and recommended for patients to engage in aerobic exercise. Patients may avoid exercise and/or rely on false safety behaviors to manage fears (e.g., checking pulse frequently, restricting speed on treadmill). While these behaviors relieve anxiety in the moment, they exacerbate and maintain anxiety long-term. Through repeated use, individuals learn to attribute “safety” to their avoidance and safety behaviors, developing false beliefs that safety is contingent upon certain actions (e.g., “It’s only safe for me to exercise when someone is monitoring my heart”), which maintain their fears and unnecessarily limits their activities (e.g., “I can’t go for a brisk walk unless someone is keeping an eye on me”). Despite theoretical and clinical relevance, there is currently no reliable and valid measure to identify and track these exercise avoidance and false safety behaviors for targeted treatment, which leaves patients vulnerable to the misperception that it is only safe to exercise under a restrictive set of circumstances and results in limited physical conditioning and functioning. This study will fill this critical assessment gap through the two following aims. Aim 1: To characterize exercise avoidance and safety behaviors in CR via comprehensive literature review, expert focus groups, and clinical behavioral observation for generation of an initial item bank to be used for development of a self-report scale. Aim 2: To refine and evaluate the psychometric properties of scale items in a sample of patients enrolled in CR through exploratory factor analysis and item reduction, followed by confirmatory factor analysis and tests of item reliability and validity in a subsequent sample. This study will have an immediate impact on efforts in promotion of CR adherence and fearless aging by developing a self- report measure of ...